1. Field of the Invention
The present invention relates to a method to from a semiconductor laser diode (hereafter denoted as LD), in particular, the invention relates to a process of the LD with a mesa structure buried by a current blocking layer with a reversely biased junction.
2. Related Prior Art
One type of an LD called as the buried hetero-structure has been well known in the fields. For instance, as disclosed in Japanese Patent Application published as JP-H08-250808A, the LD with the buried hetero-structure has an arrangement to confine the carriers by burying the mesa including an active layer and having a width of about 1 μm by the current blocking layer in both sides of the mesa.
FIG. 6 shows a cross section of the LD 200 buried with the blocking layers with a pn-junction. This LD 200 provides, on the n-type InP substrate 201, the mesa structure including the n-type InP buffer layer 202, the InGaAsP active layer 203, and the p-type InP cladding layer 204. Both sides of the mesa structure are provided with the p-type InP layer 205, the n-type InP blocking layer 206, and the p-type InP blocking layer 207. The LD 200 further provides, on the mesa and the blocking layer 207, the second p-type InP cladding layer 208, the p-type InGaAs contact layer 209, and two electrodes with the p-type 201 and the n-type 211. The LD 200 blocks the carriers injected from both electrodes, 210 and 211, by the p-type InP burying layer 205, the n-type InP blocking layer and the p-type InP blocking layer 207, which realizes the current confinement structure.
When the mesa is formed by, for instance, the wet-etching, the shape, in particular, the cross section thereof is likely deformed, which influences the distance between the active layer 203 in the mesa and the n-type InP blocking layer 206. A closer n-type InP blocking layer 206 to the n-type InP buffer layer 202 means that the carriers may easily tunnel the p-type InP burying layer 205; while, a thicker p-type InP burying layer 205 means that the holes may easily detour the active layer 203; both of which increases the leak current and degrades the emission efficiency. In order to reduce the effect described above, it is essential to reduce the scattering of the distance 200D illustrated in FIG. 6; but no substantial techniques has been known to make the distance 200D constant.